On-chip temperature sensing is an important technical feature of many integrated circuits. Temperature sensors are used to monitor temperature change for the purpose, for example, of detecting an overheating or system thermal overrun condition. Protective measures may then be taken when the temperature sensor detects an abnormal temperature condition. In another example, the output from an on-chip temperature sensor may be used to optimize the frequency of a clock signal generated by a clocking circuit or the voltage generated by a voltage generator circuit. It is critical that the output of the temperature sensor (i.e., the digital or analog signal indicative of sensed temperature) possess linearity and accuracy. For example, industrial temperature monitoring applications or temperature control loop in integrated circuits often require temperature accuracy at or in excess of 0.1° C. To accomplish this goal, it is critical that the temperature sensor be properly calibrated. Un-calibrated temperature sensors may, for example, have an accuracy of ±5° C.
The calibration of an on-chip temperature sensor typically requires the external input of a precise operating parameter such as temperature or voltage. One concern in the prior art is time required for the externally input precise operating parameter to stabilize before the calibration process can be initiated. As an example, an integrated circuit chip can be placed in a test oven for the application of a precise temperature. The time taken to bring the oven up to the desired temperature for calibration, as well as the overall process for calibration, adds significantly to the cost of chip production. This cost is further increased if the calibration operation requires multiple points of calibration input (i.e., calibration testing performed at different temperatures).
Another concern with calibration is the difficulty in controlling the accuracy of the temperature environment for calibration. In an integrated circuit production environment it is difficult and expensive to control this accuracy any better than ±1° C. The high thermal constant of such accurate calibration equipment further increases the time required to complete the calibration process, and this results in a corresponding increase in production cost.
There is accordingly a need in the art to address the foregoing issues with the calibration of an on-chip temperature sensor.